1. Field of the Invention
The present invention generally relates to computer interconnects and more particularly to using an interconnect as a cross-connect for a distributed system.
2. Description of the Related Art
Early conventional computer systems used a single interconnect, to which the various components of the computer system were connected. The interconnect known today as an Industry Standard Architecture (ISA) interconnect was used in many early computer systems. The name ISA for these interconnects was an afterwards-developed name for a previously unstandardized interconnect used in IBM PC/AT systems. With the advent of interconnects such as the Peripheral Components Interconnect (PCI) interconnect, conventional computer systems began to use a host interconnect for connecting the processor to an interconnect to connect to other components, such as adapter cards. A Host/PCI interconnect bridge typically connects the host interconnect and the PCI interconnect.
The PCI 2.2 specification, a copy of which is incorporated in its entirety by reference, allows for connecting multiple PCI interconnects in an interconnect hierarchy, with PCI-to-PCI bridges. Transactions are routed by the PCI-to-PCI bridges based on an enumeration of the interconnect hierarchy performed at initialization of the computer system. Transactions typically contain information indicating the destination interconnect number and device, which allows the bridges to determine the transaction routing.
Other interconnect architectures have been developed that can also use bridges to interconnect multiple interconnect segments. Further, the PCI-X extension to the PCI standard, as defined in the PCI-X 1.0 specification, a copy of which is incorporated herein in its entirety by reference, modifies the behavior of interconnect bridges in a PCI-X environment.
Additionally, distributed interconnects have been developed such as Ethernet, Infiband, and Fibrechannel. These distributed interconnects typically do not use bridges for connecting multiple interconnects or networks, but use devices such as routers, which route transactions across a network of connected interconnects. Typically, such distributed interconnects do not act as a single interconnect hierarchy, but as multiple connected systems.
Today, the computer industry is looking for a cost effective way to design distributed server blade type architectures. A blade server architecture typically uses an ultra dense collection of processor cards, known as “blades,” connected to a common power supply on trays in a rack. Unlike traditional multiprocessor systems, in which a single operating system manages the multiple processors in a unified execution system, a blade server system generally is a collection of independent computer systems, providing benefits such as lower power usage over traditional separately configured computer systems.
In their simplest form, a blade would be a processor and memory. However, conventional blades today are typically a full computer system, with a processor, memory, video chip, etc., all on a board getting power and Ethernet connections from a backplane. Typical blades do not contain interconnect connectors, such as a PCI connectors, because of a perceived difficulty in extending the PCI interconnect across the backplane. Because blades, by definition, are single cards, other conventional PCI devices are not typically connected via PCI slots as in typical desktop systems.
The ability to use interconnects such as PCI in blades for connection to external PCI devices has been desired, to allow reuse of existing PCI hardware and to allow reducing the number of components on the blade.